Adsorber aftertreatment system having dual soot filters

ABSTRACT

The present invention provides for adsorber catalysts arranged in parallel. The exhaust flow from the engine is divided in a predetermined ratio between the two catalysts during lean operation (e.g. 50-50). At a predetermined regeneration time (for example, when the adsorber catalyst is 20% full), the exhaust gas flow is reduced through the parallel leg that is to be regenerated (e.g. 20-80). A quantity of hydrocarbon is injected into the reduced-flow leg in order to make the mixture rich. Once the leg has been regenerated, the flow distribution between the parallel legs is reversed, and the other catalyst leg is regenerated while the other side (which is now clean) receives the majority of the exhaust flow. Once both catalyst legs have been regenerated, the exhaust flow is adjusted back to normal (e.g. 50-50) until the catalysts are again ready for regeneration and reduction. A catalytic soot filter is positioned upstream from each adsorber. The additional hydrocarbon used to promote regeneration is injected into the catalytic soot filter on the leg being regenerated. The catalytic soot filter, when used in combination with the adsorber, provides more time and surface area for the hydrocarbon to react with the oxygen. The catalytic soot filter will additionally reformulate some of the diesel fuel into hydrogen and carbon monoxide, which have been shown to be better reductants than diesel fuel.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention generally relates to internal combustionengines and, more particularly, to an NOx adsorber aftertreatment systemfor internal combustion engines.

BACKGROUND OF THE INVENTION

[0002] As environmental concerns have led to increasingly strictregulation of engine emissions by governmental agencies, reduction ofnitrogen-oxygen compounds (NOx) in exhaust emissions from internalcombustion engines has become increasingly important. Currentindications are that this trend will continue.

[0003] Future emission levels of diesel engines will have to be reducedin order to meet Environmental Protection Agency (EPA) regulated levels.In the past, the emission levels of U.S. diesel engines have beenregulated according to the EPA using the Federal Test Procedure (FTP)cycle, with a subset of more restrictive emission standards forCalifornia via the California Air Resources Board (CARB). For example,the Tier II emission standards, which are being considered for 2004, are50% lower than the Tier I standards. Car and light truck emissions aremeasured over the FTP 75 test and expressed in gm/mi. Proposed Ultra-LowEmissions Vehicle (ULEV) emission levels for light-duty vehicles up tomodel year 2004 are 0.2 gm/mi NOx and 0.08 gm/mi particulate matter(PM). Beginning with the 2004 model year, all light-duty Low EmissionVehicles (LEVs) and ULEVs in California would have to meet a 0.05 gm/miNOx standard to be phased in over a three year period. In addition tothe NOx standard, a full useful life PM standard of 0.01 gm/mi wouldalso have to be met.

[0004] Traditional methods of in-cylinder emission reduction techniquessuch as exhaust gas recirculation (EGR) and injection rate shaping bythemselves will not be able to achieve these low emission levelsrequired by the standard. Aftertreatment technologies will have to beused, and will have to be further developed in order to meet the futurelow emission requirements of the diesel engine.

[0005] Some promising aftertreatment technologies to meet future NOxemission standards include lean NOx catalysts, Selective CatalyticReduction (SCR) catalysts, and Plasma Assisted Catalytic Reduction(PACR). Current lean NOx catalyst technologies will result in thereduction of engine out NOx emissions in the range of 10 to 30 percentfor typical conditions. Although a promising technology, SCR catalystsystems require an additional reducing agent (aqueous urea) that must bestored in a separate tank, which opens issues of effective temperaturerange of storage (to eliminate freezing) as well as distribution systemsthat must be constructed for practical use of this technology. PACR issimilar to lean NOx in terms of reduction efficiency but is moreexpensive due to plasma generator. These technologies, therefore, havelimitations which may prevent their use in achieving the new emissionsrequirements.

[0006] NOx adsorber catalysts have the potential for great NOx emissionreduction (60-90%). The NOx adsorber is one of the most promising NOxreduction technologies. During lean-burn operation of the engine, thetrap adsorbs nitrogen oxide in the form of stable nitrates. Understoiciometric or rich conditions, the nitrate is thermodynamicallyunstable and the stored nitrogen oxides are released and subsequentlycatalytically reduced. Therefore, the operation cycle alternates betweenlean and rich conditions around the catalyst. During lean operation thecatalyst stores the NOx and during rich operation the NOx is releasedand reduced to N₂. However, to make the conditions around the catalystrich, a significant amount of hydrocarbon (HC) needs to be injected. Theamount of HC required for reduction is only a small fraction of thetotal hydrocarbon injected, resulting in a significant fuel penalty. Ifthe HC required to make conditions rich can be reduced, the fuel penaltycan be brought down substantially.

[0007] Furthermore, some diesel engines include a catalytic soot filterto trap the soot generated by the engine. This soot is carcinogenic toliving beings. Such catalytic soot filters often become clogged with thetrapped particulate matter owing to the fact that they require hightemperatures to regenerate. It is difficult to attain these hightemperatures in the engine exhaust stream at low loads.

[0008] There is therefore a need for an engine aftertreatment systememploying an NOx adsorber which reduces the fuel penalty associated withthese devices, allows for regeneration of the soot filter, even at lowloads, and reduces the system cost and package size. The presentinvention is directed toward meeting this need.

SUMMARY OF THE INVENTION

[0009] The present invention provides for an NOx adsorber aftertreatmentsystem for internal combustion engines which utilizes adsorber catalystsarranged in parallel. The exhaust flow from the engine is divided in apredetermined ratio between the two catalysts during lean operation(e.g. 50-50). At a predetermined regeneration time (for example, whenthe adsorber catalyst is 20% full), the exhaust gas flow is reducedthrough the parallel leg that is to be regenerated (e.g., 20% throughthe leg to be regenerated, 80% of the flow to the other leg). A quantityof hydrocarbon is injected into the reduced-flow leg in order to makethe mixture rich. Since the flow has been reduced in this leg, only asmall fraction of the amount of hydrocarbon that would have beenrequired to make the mixture rich during full flow is required. Thiswill result in a substantial reduction in the fuel penalty incurred forregeneration of the adsorber catalyst. Once the leg has beenregenerated, the flow distribution between the parallel legs isreversed, and the other catalyst leg is regenerated while the other side(which is now clean) receives the majority of the exhaust flow. Anotheradvantage of the present invention is that since NOx is being stored inone leg while the other leg is being regenerated, the regenerationoperation can be performed for a longer period of time, resulting ingreater regeneration efficiency. Once both catalyst legs have beenregenerated, the exhaust flow is adjusted back to normal (e.g. 50-50)until the catalysts are again ready for regeneration and reduction.

[0010] In one embodiment, a catalytic soot filter is positioned upstreamfrom each adsorber. The additional hydrocarbon used to promoteregeneration is injected into the catalytic soot filter on the leg beingregenerated. The catalytic soot filter, when used in combination withthe adsorber, provides more time and surface area for the hydrocarbon toreact with the oxygen. The catalytic soot filter will additionallyreformulate some of the diesel fuel into hydrogen and carbon monoxide,which have been shown to be better reductants than diesel fuel.

[0011] In one form of the invention, an internal combustion engineaftertreatment system for treating exhaust gases exiting an engine isdisclosed, the system comprising a sulfur trap having a sulfur trapinput operatively coupled to the engine exhaust and having a sulfur trapoutput, a valve system having a valve input operatively coupled to thesulfur trap output, a first valve output and having a second valveoutput, a first catalytic soot filter having a first soot filter inputoperatively coupled to the first valve output and having a first sootfilter output, a first adsorber having a first adsorber inputoperatively coupled to the first soot filter output and having a firstadsorber output, a second catalytic soot filter having a second sootfilter input operatively coupled to the second valve output and having asecond soot filter output, a second adsorber having a second adsorberinput operatively coupled to the second soot filter output and having asecond adsorber output, and a diesel oxidation catalyst having a DOCinput operatively coupled to the first and second adsorber outputs andhaving a DOC output.

[0012] In another form of the invention, an internal combustion engineaftertreatment system for treating exhaust gases exiting an engine isdisclosed, the system comprising a valve system having a valve inputoperatively coupled to the engine exhaust, a first valve output andhaving a second valve output, a first catalytic soot filter having afirst soot filter input operatively coupled to the first valve outputand having a first soot filter output, a first adsorber having a firstadsorber input operatively coupled to the first soot filter output andhaving a first adsorber output, a second catalytic soot filter having asecond soot filter input operatively coupled to the second valve outputand having a second soot filter output, and a second adsorber having asecond adsorber input operatively coupled to the second soot filteroutput and having a second adsorber output.

[0013] In another form of the invention, an internal combustion engineaftertreatment system for treating exhaust gases exiting an engine isdisclosed, the system comprising a first catalytic soot filter having afirst soot filter input operatively coupled to the engine exhaust andhaving a first soot filter output, a first adsorber having a firstadsorber input operatively coupled to the first soot filter output andhaving a first adsorber output, a second catalytic soot filter having asecond soot filter input operatively coupled to the engine exhaust andhaving a second soot filter output, and a second adsorber having asecond adsorber input operatively coupled to the second soot filteroutput and having a second adsorber output.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 is a schematic block diagram of a first preferredembodiment system of the present invention.

[0015]FIG. 2 is a schematic block diagram of a second preferredembodiment system of the present invention.

[0016]FIG. 3 is a process flow diagram illustrating a preferredembodiment process of the present invention.

[0017]FIG. 4 is a schematic block diagram of a third preferredembodiment system of the present invention.

[0018]FIG. 5 is a schematic block diagram of a fourth preferredembodiment of the present invention.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] For the purposes of promoting an understanding of the principlesof the invention, reference will now be made to the embodimentillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended, and alterations andmodifications in the illustrated device, and further applications of theprinciples of the invention as illustrated therein are hereincontemplated as would normally occur to one skilled in the art to whichthe invention relates.

[0020] Referring to FIG. 1, there is illustrated a schematic blockdiagram of a first preferred embodiment of the present invention. Thesystem is designed to remove NOx compounds from the exhaust stream of aninternal combustion engine 12, such as a diesel engine. The exhaustproduced by the engine 12 exits the exhaust manifold 14 of the engineand is passed through an optional sulfur trap 16. NOx adsorber catalystsare extremely sensitive to the level of sulfur in the fuel. The fuel andthe lubrication oil of the engine contain sulfur and thereforesulfur-oxygen compounds (SOx) are contained in the exhaust gas. This SOxis adsorbed into the NOx adsorber and reduces its capacity. Unlike NOx,SOx does not regenerate under rich conditions within the operatingtemperature range of the engine. Eventually the adsorber is filled upwith sulfate and becomes inactive. The optional sulfur trap 16 maytherefore be used to trap SOx compounds before they reach the NOxadsorbers downstream.

[0021] The output of the sulfur trap 16 may be passed through anoptional catalytic soot filter 18 in order to trap any diesel sootparticulate matter that may be entrained in the exhaust gases. Inaddition to trapping diesel soot particulate matter by physicalfiltering, the catalytic soot filter also acts as a flow-throughoxidation catalyst by the addition of precious metal catalysts whichreduce the volatile organic fraction of the soot material by thecatalyzed oxidation reaction (e.g. C+Oxidant→CO). A sensor 20 may beplaced at the output of the soot filter 18 in order to measure thetemperature and air/fuel (A/F) ratio (lambda) of the exhaust stream. Theoutput of the optional sensor 20 is provided to an electronic enginecontrol module 22.

[0022] The engine controller 22 is additionally coupled to the engine 12for reading various engine sensor data, such as engine position sensordata, speed sensor data, air mass flow sensor data, fuel rate data,etc., as is known in the art. The engine controller 22 may furtherprovide data to the engine 12 in order to control the operating state ofthe engine 12, as is well known in the art.

[0023] The flow of exhaust leaving the soot filter 18 is controlled by aproportional control 3-way valve 24. As is known in the art, aproportional control 3-way valve may be used to divide the flow of a gasstream into two separate paths, wherein the percentage of the total gasflow being directed to either path is controllable. In the embodiment ofFIG. 1, the proportional control 3-way valve 24 is coupled to the enginecontroller 22 in order to control the relative proportions of exhaustgas flow routed to either output of the valve 24.

[0024] The two outputs of the valve 24 are coupled to the respectiveinputs of a pair of NOx adsorbers (catalytic converters) 26 and 28.Therefore, by providing control signals from the engine controller 22 tothe proportional control 3-way valve 24, the percentage of the totalexhaust flow from the engine 14 entering either the adsorber 26 or theadsorber 28 may be precisely controlled. A fuel injector 30 ispositioned to inject a measured quantity of fuel (hydrocarbon) into theexhaust gas flow entering the adsorber 26. Similarly, a second fuelinjector 32 is positioned to inject a quantity of fuel into the exhaustgas flow entering adsorber 28. Both injectors 30, 32 are controlled bythe engine controller 22 and are supplied with fuel from a pump 34supplied by the vehicle fuel tank 36. Preferably, the fuel pump 34 is alow-cost diaphragm-type fuel pump. Two igniters 38 are provided toignite the fuel being injected by the injectors 30, 32 under the controlof the engine controller 22.

[0025] Because the exhaust flow is reduced in the adsorber leg beingregenerated, the amount of reductant required to bum off the oxygenreduces. The concentration of reductant required for reduction remainsthe same, but this amount is a small fraction of the total reductantduring full exhaust flow. It will be appreciated that any flow ratiosmay be utilized during reduction and regeneration and during normalflow, even though exemplary flows are used herein for illustrativepurposes. The optimum flow ratios for any given system will depend uponthe particular system configuration.

[0026] The exhaust gases exiting the adsorbers 26 and 28 are combinedtogether before being input to an optional diesel oxidation catalyst 40.Due to the pulse injection of relatively large quantities of reductant(normally hydrocarbon) for short periods during regeneration of the NOxadsorbers 26, 28 of the present invention, some unburned hydrocarbon canslip through the adsorber catalyst. The use of a diesel oxidationcatalyst 40 downstream of the adsorbers 26, 28 virtually eliminateshydrocarbon emission from the tailpipe. Such catalysts contain preciousmetals in them that reduce the activation energy of hydrocarboncombustion, such that the unburned hydrocarbon is oxidized to carbondioxide and water. The exhaust gases exiting the diesel oxidationcatalyst 40 may then exit the vehicle. An optional NOx sensor 42 may beplaced between the adsorbers 26, 28 and the diesel oxidation catalyst 40in order to directly measure the NOx levels leaving the adsorbers 26 and28. The output of the optional NOx sensor 42 is provided to the enginecontroller 22.

[0027] Referring now to FIG. 2, there is illustrated a second preferredembodiment of the present invention. The second embodiment of thepresent invention is similar to the first embodiment illustrated in FIG.1, and like reference designators refer to like components. In thesecond embodiment, the proportional control 3-way valve is replaced witha pair of two-way valves 50 and 52. Valve 50 controls the flow ofexhaust gases into the adsorber 26, while valve 52 controls the flow ofexhaust gases into adsorber 28. Each of the vaives 50, 52 is coupled tothe engine controller 22 for control thereby.

[0028] The valves 50, 52 may comprise either variable flow rate controlvalves or may comprise valves having a fixed number of flow ratesettings. For example, if the aftertreatment system design dictates thatthe relative flow between adsorbers 26, 28 will always be 20-80 duringregeneration, then the valves 50, 52 may have discrete settings thatwill allow the engine controller 22 to switch them between reduced flow(20%) and max flow (80%) settings in order to achieve the desired flowreduction in one of the adsorbers 26, 28. Optionally, the valves 50, 52may have variably adjustable flow rates, such that the engine controller22 can infinitely adjust the flow percentage through each valve 50, 52in order to divide the exhaust flow between the adsorbers 26, 28 in anydesired proportion.

[0029] Referring now to FIG. 3, there is illustrated a preferredembodiment process of the present invention. The process begins at step100, which represents the steady state operation of the engine withexhaust gas flow split evenly between the adsorbers 26 and 28. At step102, the engine controller 22 determines whether either of the adsorber26, 28 catalysts need be regenerated. The decision made at step 102 canbe made under open-loop control, by using stored catalyst adsorptionmaps in the engine controller 22. These catalyst adsorption maps may bepredetermined using empirical data from laboratory tests utilizing thesame or similar engine and exhaust system. The regeneration decision atstep 102 may also be made under closed-loop control, wherein the enginecontroller 22 examines the data being produced by the NOx sensor 42which is proportional to the level of NOx being emitted at the output ofthe adsorbers 26, 28.

[0030] If step 102 determines that the adsorbers 26, 28 need to beregenerated (e.g. the adsorption efficiency has dropped to 80%), thenthe process continues at step 104 in which the flow of exhaust throughthe system is controlled such that the adsorber to be regeneratedreceives a reduced level of exhaust flow. For example, if the enginecontroller 22 determines that adsorber 26 needs to be regenerated, thenthe flow of exhaust through the adsorber 26 can be reduced to 20% of thetotal exhaust flow, with the remaining 80% being routed through theadsorber 28. The relative proportions of exhaust flow routed to eitheradsorber will depend upon various system design parameters. The 20-80split discussed herein is for illustrative purposes only.

[0031] Control of the relative flow of exhaust gases through adsorbers26 and 28 is performed under control of the engine controller 22 (forexample, based upon the engine sensor parameters being sent to thecontroller 22 (engine position sensor, speed sensor, air mass flowsensor, fuel rate, etc.)) through operation of either the proportionalcontrol 3-way valve 24 of the system of FIG. 1 or through control of thedual 2-way valves 50, 52 of the system of FIG. 2, which are adjusted toachieve the correct predetermined exhaust flow velocity needed forregeneration of the aftertreatment system.

[0032] Once the correct flow velocity has been achieved through each ofthe adsorbers 26, 28, the process moves to step 106 in which the enginecontroller 22 determines the temperature and air/fuel ratio of theregeneration exhaust stream using the sensor 20. If the temperature ofthe exhaust stream is sufficient for regeneration of the catalysts(according to a predetermined temperature limit), then the processcontinues to step 110. If step 106 determines that the temperature ofthe regeneration exhaust stream needs to be raised, then the processcontinues at step 108 in which the engine controller 22 causes theigniter 38 to be activated in order to ensure ignition of theregeneration fuel injection.

[0033] At step 110, the fuel injector 30, 32 in the leg beingregenerated is used to inject the required amount of fuel into theexhaust stream as a reductant to completely regenerate the catalystswithin the adsorber. The injectors 30, 32 are controlled by the enginecontroller 22. The exhaust fuel injector 30, 32 is used to achieve arich air/fuel ratio (lambda less than 1.0) in the regeneration stream.Because of the reduced amount of exhaust gas flowing through theregeneration leg, the quantity of fuel needed to be injected by theinjector 30, 32 is greatly reduced, thereby significantly reducing thefuel penalty associated with adsorber regeneration. This injected fuelwill be ignited by the temperature of the exhaust gas stream (possiblysupplemented by the igniter 38) in order to facilitate regeneration ofthe adsorber.

[0034] Once regeneration of the leg is determined to be complete at step112 (e.g. after a predetermined amount of time has elapsed), the processcontinues at step 114, where the engine controller 22 determines if bothlegs of the system have been regenerated. If they have not, then theprocess continues at step 116, where the engine controller 22 operateseither the proportional control 3-way valve 24 or the 2-way valves 50,52 in order to route the majority of the exhaust gas flow to therecently regenerated leg and to reduce the amount of exhaust gasesflowing through the leg which is to be regenerated. The process is thenreturned to step 106 in order to regenerate the next leg. If, on theother hand, step 114 determines that both legs have been regenerated,then the process is returned to step 100 where the engine controller 22operates the proportional control 3-way valve 24 or the 2-way valves 50,52 in order to evenly split the exhaust gas flow through the adsorbers26, 28.

[0035] As detailed hereinabove, the adsorber regeneration cycle switchesback and forth between the two sides of the exhaust as necessary inorder to keep the outlet exhaust stream purified of excessive emissions.It will be appreciated that since dual exhaust streams are beingutilized, the regeneration cycle of the adsorber does not necessarilyhave to be short. During the entire time that the adsorber is beingregenerated, the second adsorber is available for cleaning the majorityof the exhaust gas stream. It should also be noted that the temperatureof the regeneration exhaust gas stream may also be controlled byadjustment of the proportional control 3-way valve in conjunction withthe igniter 38. By allowing slightly more exhaust gas to pass into theregeneration side of the exhaust, the temperature thereof may be raised.

[0036] Besides the aforementioned advantages in adsorber regeneration,the arrangement of catalysts illustrated in FIGS. 1 and 2 of the presentinvention provides other benefits. Placing the catalytic soot filter 18before the adsorbers 26, 28 helps in multiple ways. The catalytic sootfilter 18 converts the NO in the exhaust stream to NO₂ which helps NOxstorage in the adsorber 26, 28. The catalytic soot filter 18 alsoprevents particulate matter from clogging the adsorber system and italso helps increase the temperature of the exhaust stream in order tomake the adsorber 26, 28 more efficient.

[0037] In another embodiment, the sulfur trap 16 may be placeddownstream from the catalytic soot filter 18. By placing the catalyticsoot filter 18 upstream of the sulfur trap 16, the catalytic soot filter18 will convert SO₂ to SO₃, which is more readily trapped by the sulfurtrap 16.

[0038] Therefore, the system illustrated and described herein iseffective in addressing all legislatively-controlled emissions includingNOx, SOx and hydrocarbons. The adsorbers are used for reduction of NOxlevels and are more easily regenerated than in prior art systems. Thesulfur trap removes sulfur from the exhaust, making the operation of theadsorber more efficient and longer lasting. The catalytic soot filtertraps particulate soot from the exhaust stream. Finally, the dieseloxidation catalyst cleans up any leftover hydrocarbons exiting theadsorbers, thereby allowing the exhaust emitted by the system of thepresent invention to meet or exceed the requirements of the variouslegislative bodies.

[0039] Referring now to FIG. 4, there is illustrated a third preferredembodiment of the present invention. The third embodiment of the presentinvention is similar to the first embodiment illustrated in FIG. 1, andlike reference designators refer to like components. In the thirdembodiment, the catalytic soot filter 18 is replaced with a pair ofcatalytic soot filters 18 a, 18 b. The catalytic soot filter 1 8a ispositioned upstream from the adsorbers 26, while the catalytic sootfilter 18 b is positioned upstream from the adsorber 28.

[0040] As discussed hereinabove, catalytic soot filters 18 require hightemperatures in order to regenerate. It is difficult to attain thesehigh temperatures in the exhaust stream during low load operation of theengine 12. Under these conditions, the soot filter 18 eventually becomesclogged with soot. By placing the soot filters 18 a, 18 b upstream fromthe adsorbers 26, 28 and downstream from the fuel injectors 30,32 asshown in the third embodiment, the catalytic soot filters 18 a, 18 balso receive the injected hydrocarbon and are regenerated by combustionof this hydrocarbon. Placement of the catalytic soot filters 18 a, 18 bin this position also provides more time and surface area for theintroduced hydrocarbon to react with oxygen, thereby more completelyburning the hydrocarbon. More complete hydrocarbon combustion willpossibly eliminate the need for the diesel oxidation catalyst 40,thereby reducing exhaust system cost and package size.

[0041] Furthermore, the catalytic soot filters 18 a, 18 b willreformulate some of the diesel fuel into hydrogen and carbon monoxide,which have been shown to be better reductants than diesel fuel. Thisimprovement in reduction will result in more complete regeneration ofthe catalytic soot filers 18 a, 18 b and adsorbers 26, 28 and/or ashorter regeneration time.

[0042] A fourth preferred embodiment of the present invention isillustrated in FIG. 5. The fourth preferred embodiment is a modificationof the second preferred embodiment of FIG. 2, in which the catalyticsoot filter 18 is replaced with a catalytic soot filter 18 a, 18 bpositioned in each adsorber leg, upstream from the adsorbers 26, 28 anddownstream from the fuel injectors 30, 32. These modifications are madefor the same reason explained hereinabove with respect to the thirdpreferred embodiment, and the same desirable effects are achieved.

[0043] While the invention has been illustrated and described in detailin the drawings and foregoing description, the same is to be consideredas illustrative and not restrictive in character, it being understoodthat only the preferred embodiment has been shown and described and thatall changes and modifications that come within the spirit of theinvention are desired to be protected.

We claim:
 1. An internal combustion engine aftertreatment system fortreating exhaust gases exiting an engine, the system comprising: asulfur trap having a sulfur trap input operatively coupled to the engineexhaust and having a sulfur trap output; a valve system having a valveinput operatively coupled to the sulfur trap output, a first valveoutput and having a second valve output; a first catalytic soot filterhaving a first soot filter input operatively coupled to the first valveoutput and having a first soot filter output; a first adsorber having afirst adsorber input operatively coupled to the first soot filter outputand having a first adsorber output; a second catalytic soot filterhaving a second soot filter input operatively coupled to the secondvalve output and having a second soot filter output; a second adsorberhaving a second adsorber input operatively coupled to the second sootfilter output and having a second adsorber output; and a dieseloxidation catalyst having a DOC input operatively coupled to the firstand second adsorber outputs and having a DOC output.
 2. The system ofclaim 1, further comprising: a supply of fuel; a pump having a pumpinlet operatively coupled to the supply of fuel and having a pumpoutlet; a first fuel injector having a first injector input operativelycoupled to the pump outlet and having a first injector outputoperatively coupled to the first soot filter input; and a second fuelinjector having a second injector input operatively coupled to the pumpoutlet and having a second injector output operatively coupled to thesecond soot filter input.
 3. The system of claim 1, further comprising:An ignitor operatively coupled to the first and second soot filterinputs.
 4. The system of claim 1, further comprising: a temperature andlamda sensor having a sensor input operatively coupled to the sulfurtrap output.
 5. The system of claim 1, further comprising: an NOx sensorhaving an NOx sensor input operatively coupled to the first and secondadsorber outputs.
 6. The system of claim 1, wherein the valve systemcomprises a proportional control 3-way valve.
 7. The system of claim 1,wherein the valve system comprises a pair of 2-way valves.
 8. Aninternal combustion engine aftertreatment system for treating exhaustgases exiting an engine, the system comprising: a valve system having avalve input operatively coupled to the engine exhaust, a first valveoutput and having a second valve output; a first catalytic soot filterhaving a first soot filter input operatively coupled to the first valveoutput and having a first soot filter output; a first adsorber having afirst adsorber input operatively coupled to the first soot filter outputand having a first adsorber output; a second catalytic soot filterhaving a second soot filter input operatively coupled to the secondvalve output and having a second soot filter output; and soot filteroutput and having a second adsorber output.
 9. The system of claim 8,further comprising: a sulfur trap having a sulfur trap input operativelycoupled to the engine exhaust and having a sulfur trap outputoperatively coupled to the valve input.
 10. The system of claim 8,further comprising: a diesel oxidation catalyst having a DOC inputoperatively coupled to the first and second adsorber outputs and havinga DOC output.
 11. The system of claim 8, further comprising: a supply offuel; a pump having a pump inlet operatively coupled to the supply offuel and having a pump outlet; a first fuel injector having a firstinjector input operatively coupled to the pump outlet and having a firstinjector output operatively coupled to the first soot filter input; anda second fuel injector having a second injector input operativelycoupled to the pump outlet and having a second injector outputoperatively coupled to the second soot filter input.
 12. The system ofclaim 8, further comprising: an ignitor operatively coupled to the firstand second soot filter inputs.
 13. The system of claim 8, furthercomprising: a temperature and lamda sensor having a sensor inputoperatively coupled to the valve input.
 14. The system of claim 8,further comprising: an NOx sensor having an NOx sensor input operativelycoupled to the first and second adsorber outputs.
 15. The system ofclaim 8, wherein the valve system comprises a proportional control 3-wayvalve.
 16. The system of claim 8, wherein the valve system comprises apair of 2-way valves.
 17. An internal combustion engine aftertreatmentsystem for treating exhaust gases exiting an engine, the systemcomprising: a first catalytic soot filter having a first soot filterinput operatively coupled to the engine exhaust and having a first sootfilter output; a first adsorber having a first adsorber inputoperatively coupled to the first soot filter output and having a firstadsorber output; a second catalytic soot filter having a second sootfilter input operatively coupled to the engine exhaust and having asecond soot filter output; and a second adsorber having a secondadsorber input operatively coupled to the second soot filter output andhaving a second adsorber output.
 18. The system of claim 17, furthercomprising: an ignitor having an ignitor output operatively coupled tothe first and second soot filter inputs.
 19. The system of claim 17,further comprising: a sulfur trap mounted between the engine and thefirst and second soot filter inputs for flow of exhaust gastherethrough.
 20. The system of claim 17, further comprising: a valvesystem having a valve input operatively coupled to the engine exhaust, afirst valve output operatively coupled to the first soot filter inputand having a second valve output operatively coupled to the second sootfilter input.
 21. The system of claim 17, further comprising: a supplyof fuel; a pump having a pump inlet operatively coupled to the supply offuel and having a pump outlet; a first fuel injector having a firstinjector input operatively coupled to the pump outlet and having a firstinjector output operatively coupled to the first soot filter input; anda second fuel injector having a second injector input operativelycoupled to the pump outlet and having a second injector outputoperatively coupled to the second soot filter input.
 22. The system ofclaim 19, further comprising: a temperature and lamda sensor having asensor input operatively coupled to the sulfur trap output.
 23. Thesystem of claim 17, further comprising: an NOx sensor having an NOxsensor input operatively coupled to the first and second adsorberoutputs.
 24. The system of claim 20, wherein the valve system comprisesa proportional control 3-way valve.
 25. The system of claim 20, whereinthe valve system comprises a pair of 2-way valves.
 26. The system ofclaim 17, further comprising: a diesel oxidation catalyst having a DOCinput operatively coupled to the first and second adsorber outputs andhaving a DOC output.